dullness vs jejunity

dullness and jejunity both are nouns.

Word	Noun	Adjective	Verb	Adverb
dullness	Yes	No	No	No
jejunity	Yes	No	No	No

As nouns, jejunity is a hyponym of dullness; that is, jejunity is a word with a more specific, narrower meaning than dullness:

dullness (noun)	jejunity (noun)
lack of sensibility	the quality of being vapid and unsophisticated
without sharpness or clearness of edge or point	quality of inadequate nutritive value
the quality of lacking interestingness
a lack of visual brightness
the quality of being slow to understand